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Science et changements planétaires / Sécheresse. Volume 5, Number 3, 191-8, Septembre 1994, Synthèse

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Author(s) : Christian Valentin

Summary : Although annual rainfall has decreased in the Sahel since the late sixties, the same has not applied to erosive, high-intensity rainfall. These intense storms result in slaking of surface soil aggregates. The detached particles are either removed by wind or water erosion or rearranged within a short distance to form a surface crust. Along with drought and the decline in plant cover and soil organic matter content, these crusts have spread considerably. The processes involved, albeit natural, have been accelerated by human activities. The removal of top-layers and subsequent exposure of the gravelly layers beneath is mostly found in areas where the land has been overgrazed or cleared for cultivation. The spread of crusts has triggered off an increase in runoff coefficients, no matter what the scale of measurement: from 1 m2 to small watershed. Similarly, drought has also resulted in increased rill and wind erosion and hence the frequency of dust haze. These processes - surface crusting, water and wind erosion - are all closely interlinked.

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